Field of the Invention
The present invention relates to hydraulic circuits used for controlling drive of continuously variable transmissions.
Description of Related Art
As an electric power generating device for an aircraft, it is known to use a constant frequency generator (IDG) which operates while keeping a rotation rate (frequency) thereof constant even when a rotation rate of an aircraft engine, which is a drive source, varies. As a transmission for keeping the rotation rate of the generator constant in the IDG, a continuously variable transmission has been used.
The continuously variable transmission is controlled by hydraulic pressure. If a hydraulic circuit is not supplied with a sufficient amount of oil when gravitational acceleration of a flying aircraft changes from positive to negative (or vice versa), operation of the continuously variable transmission may become unstable. In order to avoid such a situation, it has been proposed to provide an oil return line for returning a predetermined amount of oil to an upstream side of an oil supply pipe, thereby to compensate for shortage of oil, and cause the continuously variable transmission to stably operate (refer to Patent Document 1, for example).